Due to the environmental effects caused by air pollution and exhaustion of fossil fuels, a driving apparatus using an electric motor is highlighted. Thus, a hybrid vehicle using an engine as a main power source and an electric motor as an auxiliary power source has been developed and commercialized. Further an electric vehicle using an electric motor as a main power source is under development. In this reason, an electric motor providing higher output is more demanded.
FIG. 16 is a schematic view of a conventional motor. A conventional motor includes a central shaft 1, a stator 5 and a rotor 3. The rotor 3 includes a yoke 4 and permanent magnets 2 fixed to the yoke 4 and is rotatably coupled with a central shaft 1 by means of a bearing. The permanent magnets 2 are coupled with the yoke 4 with opposite polarities.
The stator 5 is formed by winding a coil around an armature metal core and fixedly coupled to the central shaft 1. Also, if an electric current is supplied to the coil, a magnetic field is generated around the coil. Thus, the magnetic field generated around the coil interacts with a magnetic field of the permanent magnet 2 to generate magnetomotive force, and the magnetomotive force causes the rotor 3 to rotate about the central shaft 1.